Leader of the Photonic Nanomaterials Group (PNG) in which research is focused on optical and electronic properties of solid state nanostructures for applications such as optoelectronics devices, quantum information processing and photovoltaics. At present the Group’s research involves two such systems - semiconductor nanocrystals and colour centres in diamond which we investigate using luminescence-based optical techniques. More information about our research can be found on the PNG website.
Laser writing of individual nitrogen-vacancy defects in diamond with near-unity yield
Laser writing of individual atomic defects in a crystal with near-unity yield
Atomic defects in wide band gap materials show great promise for development
of a new generation of quantum information technologies, but have been hampered
by the inability to produce and engineer the defects in a controlled way. The
nitrogen-vacancy (NV) color center in diamond is one of the foremost
candidates, with single defects allowing optical addressing of electron spin
and nuclear spin degrees of freedom with potential for applications in advanced
sensing and computing. Here we demonstrate a method for the deterministic
writing of individual NV centers at selected locations with high positioning
accuracy using laser processing with online fluorescence feedback. This method
provides a new tool for the fabrication of engineered materials and devices for
quantum technologies and offers insight into the diffusion dynamics of point
defects in solids.
quant-ph, quant-ph, cond-mat.mes-hall
Single Nitrogen-Vacancy Imaging in Nanodiamonds for Multimodal Sensing
Driven-dissipative non-equilibrium Bose–Einstein condensation of less than ten photons
Valley coherent exciton-polaritons in a monolayer semiconductor.
Two-dimensional transition metal dichalcogenides (TMDs) provide a unique possibility to generate and read-out excitonic valley coherence using linearly polarized light, opening the way to valley information transfer between distant systems. However, these excitons have short lifetimes (ps) and efficiently lose their valley coherence via the electron-hole exchange interaction. Here, we show that control of these processes can be gained by embedding a monolayer of WSe2 in an optical microcavity, forming part-light-part-matter exciton-polaritons. We demonstrate optical initialization of valley coherent polariton populations, exhibiting luminescence with a linear polarization degree up to 3 times higher than displayed by bare excitons. We utilize an external magnetic field alongside selective exciton-cavity-mode detuning to control the polariton valley pseudospin vector rotation, which reaches 45° at B = 8 T. This work provides unique insight into the decoherence mechanisms in TMDs and demonstrates the potential for engineering the valley pseudospin dynamics in monolayer semiconductors embedded in photonic structures.
Formation of a macroscopically occupied polariton state in a tunable open-access microcavity under resonant excitation
Microcavity enhanced single photon emission from two-dimensional WSe2
APPLIED PHYSICS LETTERS
Robust, tunable, and high purity triggered single photon source at room temperature using a nitrogen-vacancy defect in diamond in an open microcavity.
We report progress in the development of tunable room temperature triggered single photon sources based on single nitrogen-vacancy (NV) centres in nanodiamond coupled to open access optical micro-cavities. The feeding of fluorescence from an NV centre into the cavity mode increases the spectral density of the emission and results in an output stream of triggered single photons with spectral line width of order 1 nm, tunable in the range 640 - 700 nm. We record single photon purities exceeding 96% and estimated device efficiencies up to 3%. We compare performance using plano-concave microcavities with radii of curvature from 25 μm to 4 μm and show that up to 17% of the total emission is fed into the TEM00 mode. Pulsed Hanbury-Brown Twiss (HBT) interferometry shows that an improvement in single photon purity is facilitated due to the increased spectral density.
Strong coupling between 0D and 2D modes in optical open microcavities